Heat exchangers are employed throughout various installations in different industries with the primary purpose of gaining or rejecting heat. Some of the most common applications of heat exchangers are found in condensers and evaporators for air conditioning systems and production plants. They are also used in other industries like power plants, refineries, desalination plants and petrochemical installations.
Typically, heat exchange systems achieve the purpose of heat transfer by circulating fluid through a bundle of tubes in the system. The nature of fluids flowing within the tubes can result in fouling, for example accumulation of debris, biological growth, build-up of scale and corrosion. As a result, periodic cleaning of the tubes is essential to maintain optimal performance of the heat exchange system. Techniques of tube cleaning are broadly categorized into on-line and off-line methods.
Off-line cleaning methods, for example rod-and-brush method, chemical cleaning method and high-pressure water jetting method, involve an external cleaning process that requires shutting down the entire heat exchange system before cleaning can be initiated. These off-line cleaning methods are time consuming and labour intensive which make them undesirable for installations requiring short turn-around time. In contrast, on-line cleaning methods utilize cleaning systems that clean heat exchanger tubes while the heat exchange system is in continuous operation. On-line cleaning methods are normally automatic, rendering an extended continuous length run between each regular maintenance shutdown. Hence, they are suitable for implementation into installations that either operates for long hours or sensitive to long system shutdown time.
One type of on-line cleaning method involves circulating multiple foam balls through the heat exchange system, whereby the foam balls will remove and push out fouling deposits in every tube they travel through. U.S. Pat. No. 5,520,712 disclosed an abrasive cleaning ball made from sponge rubber material and constituted by short lengths of abrasive material. J.P. Pat. No. 58,244,423 discloses another type of cleaning ball with an oval spherical shape containing fibers. In J.P. Pat. No. 58,016,125, fibers are fixed on a hollow cleaning ball having small holes. This type of cleaning ball was claimed to be much better than conventional sponge ball with respect to the displacement of water and air. Although the aforesaid cleaning balls are used in cleaning conventional tubes with smooth internal surfaces, they may not be as effective in cleaning evolutionary heat exchange systems that employ enhanced tubes.
Traditionally, tubes used in heat exchange systems are manufactured with a smooth internal surface (smooth bore). With the advancement of heat transfer technologies, new features are incorporated onto the tubes to improve the performance and efficiency of heat exchange systems. These hew improved tubes are known as enhanced tubes and super enhanced tubes. In contrast with the conventional smooth bore tubes, the enhanced tubes have an internal “rifling” feature, which is basically a spiral groove inside the tube. The spiral groove provides more surface area for heat transfer and creates more turbulence in the fluid passing through the tubes. In addition, the enhanced tubes have thinner tube walls in comparison with conventional tubes so as to provide a more efficient overall heat transfer.
Efficiency of the heat exchange system is determined by the cleanliness of the heat transfer surfaces of the tubes. In order to maintain the efficiency and life span of the heat exchange system, it is vital to remove any fouling within the tubes. Over the years, the improvement in heat transfer rates by enhancing the tubes has greatly increased the performance and efficiency of heat exchange systems. However, cleaning these enhanced tubes is more difficult and complicated due to its internal spiral groove. The enhanced tubes are more prone to foulings. Their thin tube walls are also more susceptible to localized pitting failure due to microbiologically influenced corrosion (MIC) and under-deposit corrosion. To prevent these types of corrosion, cleaning of the tubes must be constantly and consistently implemented in order to remove the foulings as they occur.
Currently, conventional foam balls are not effective in removing the foul deposits formed on the spiral grooves of internal rifling in enhanced tubes. The conventional foam balls merely translate through the tubes and do not provide positive physical contact to the spiral grooves to effectively remove any foul deposits accumulated there. In order to fully harness the advantages of an on-line cleaning method, there is an imperative need to have a device that is capable of cleaning the spiral grooves of enhanced tubes efficiently and effectively. This invention satisfies this need by disclosing a device for cleaning tubes, in particular enhanced tubes. Other advantages of this invention will be apparent with reference to the detailed description.